When the richest man in the city is also the one who runs it. An assessment of an extraordinary era.

It was clear from the very beginning that Michael Bloomberg was taking us to a different political universe. A novice candidate who had barely won office with 50.7 percent of the vote, he had spent the first months of 2002 in City Hall closing a nearly $5 billion budget deficit. That was why he’d been elected, to make tough managerial choices as a recession accelerated and the city tried to rebound from a devastating terrorist attack. Yet the following year’s budget crisis was sure to be worse—a property-tax increase appeared inevitable, maybe one as high as 25 percent. New York’s middle class and poor were already taking a beating and, in his determination to move the city past the tragedy of 9/11, Bloomberg had started to antagonize victims’ families. So with his honeymoon beginning to fade, the multibillionaire mayor was choosing this moment to insist that one of his most urgent priorities was … banning smoking in restaurants and bars?

“It was totally voluntary. You don’t need to take on that fight, and it’s politically harmful,” says Ed Skyler, Bloomberg’s first-term press secretary. “The property tax and the smoking ban at the same time, it made him seem sort of anti–middle class, anti–working class. Politically, it was a bad combination.”

But Michael Bloomberg didn’t care. Smoking killed. And besides, Bloomberg had lured his public-health commissioner, Dr. Thomas Frieden, from an important post battling tuberculosis in India by promising to eradicate smoking in the city. The mayor was going to stick to that promise, and the sooner he followed through, the more lives he would save. But Frieden, who had worked in city government before, was still somewhat skeptical that Bloomberg would follow through. “So I said, ‘But Mr. Mayor, I do want to warn you that this is going to be really controversial; they are going to be attacking you, it’s going to be very unpleasant,’’ Frieden says. “And he interrupted me and said, ‘Do you know what the first rule of sales is?’ And I said, ‘No, no I don’t.’ And he says, ‘The first rule of sales is: Once you’ve made the sale, leave.’ And then he laughed.”

Now it was Bloomberg who needed to make the sale. He’d defied the laws of political gravity once already, winning control of the city’s public schools. But smoking was different. Bloomberg needed a law to be passed by the City Council.

Bloomberg brandished statistics about increasing life expectancy, and his aides testified in public hearings—all the standard old-politics moves. But he had spent $74 million to get elected. Now like-minded outside groups that had already been or soon would be recipients of Bloomberg’s charitable millions, like the Campaign for Tobacco-Free Kids, sprang into action. Radio ads from the city’s Health Department soon appeared. Petition drives in support of the ban were launched. A poll showed broad support for the idea.

By December, New York had the toughest anti-smoking law of any big city—something few in the city had wanted, until Michael Bloomberg decided to give it to them.

The smoking ban was, like many of the mayor’s initiatives, beyond politics. His wealth, and the habits of mind that accompanied it, allowed him to be his own ­constituency. Under Michael Bloomberg, the old politics of tribal shouting and horse-trading didn’t disappear completely—but the mayor’s way of playing raw politics was handing the state’s Independence Party more than $1 million when he needed a ­ballot line, for instance. Bloomberg sold himself as a postpartisan technocrat, yet the hallmarks of his governing style turned out to be simpler and more personal: By temperament and habit and bank account, he could choose what he wanted to listen to. And what he didn’t want to hear was noise. Most often, the old clamor of New York’s traditional political machinery was a disturbance heard at a distance, replaced by an obsession with data and money and pure Bloombergian idiosyncrasy.

There was, often, little balancing of interests or conciliation of stakeholders, the sorts of things that even Rudy Giuliani had to indulge in from time to time. Instead, there was an emphasis on the long-term, and rationality—“the merits,” as defined by the mayor. His core independence from the old political forces enabled Bloomberg to undertake acts of political bravery that benefited millions: He was autocratic for the people. Yet that independence could swell into imperiousness, like 2008’s term-limits extension, a high-handedness that is haunting the current campaign to succeed him and is likely to leave its own lasting mark on New York’s politics.

The city, back in 2001, thought it was electing a new mayor. Bloomberg, for two years of his reign its richest citizen, believed the city had installed him as its new boss. He would make New York a magnet for the 21st-century economy, a winner in the global competition among cities, and save us from ourselves, if we would only let him. The specific admixture of wealth and arrogance and brains and political innocence that bent the city’s valences to his ends will be impossible to re-create. No matter who wins in November, Michael Bloomberg’s greatest feat—the way he upended the city’s entire political system—may also turn out to be his most ephemeral.